To measure the interaction of electromagnetic radiation with fluids in a measuring cell, there must be permeable and transparent windows in the measuring cell for the region of the electromagnetic spectrum which is relevant to the measurement. The windows must seal a measurement space of the measuring cell relative to the environment, even at possibly higher pressures. This applies especially to inline measuring cells.
In particular for absorption measurements it is necessary to know exactly the resulting layer thickness or the optical path length along the beam path of the electromagnetic radiation in order to be able to evaluate the measured values accordingly.
In many measurement applications it is necessary to clean the measuring cell often and/or to make available another layer thickness. In the past, different measuring cells were used for this purpose or various inserts for different layer thicknesses were provided.
U.S. Pat. No. 5,905,271 discloses a measuring cell with a complex mechanical structure in which the adjustment of the optical path length, therefore of the distance between the windows, is enabled in a very small region (by compression of the seal 31 on the stop 22).